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.Dd Oct 19, 2004
.Dt SETXATTR 2
.Os "Mac OS X"
.Sh NAME
.Nm setxattr,
.Nm fsetxattr
.Nd set an extended attribute value
.Sh SYNOPSIS
.Fd #include <sys/xattr.h>
.Ft int
.Fn setxattr "const char *path" "const char *name" "void *value" "size_t size" "u_int32_t position" "int options"
.Ft int
.Fn fsetxattr "int fd" "const char *name" "void *value" "size_t size" "u_int32_t position" "int options"
.Sh DESCRIPTION
Extended attributes extend the basic attributes associated with files and
directories in the file system.  They are stored as name:data pairs
associated with file system objects (files, directories, symlinks, etc).
.Pp
.Fn setxattr
associates
.Fa name
and
.Fa data
together as an attribute of
.Fa path .
.Pp
An extended attribute's
.Fa name
is a simple NULL-terminated UTF-8 string.
.Fa Value
is a pointer to a data buffer of
.Fa size
bytes containing textual or binary data to be associated with the
extended attribute.
.Fa Position
specifies the offset within the extended attribute.  In the current
implementation, only the resource fork extended attribute makes use of
this argument.  For all others,
.Fa position
is reserved and should be
set to zero.
.Pp
.Fa options
controls how the attribute is set:
.Pp
.Bl -tag -width XATTR_NOFOLLOW
.It Dv XATTR_NOFOLLOW
do not follow symbolic links.
.Fn setxattr
normally sets attributes on the target of
.Fa path
if it is a symbolic link.
With this option,
.Fn setxattr
will act on the link itself.
.It Dv XATTR_CREATE
fail if the named attribute already exists.
.It Dv XATTR_REPLACE
fail if the named attribute does not exist.  Failure to specify
.Dv XATTR_REPLACE
or
.Dv XATTR_CREATE
allows creation and replacement.
.El
.Pp
.Fn fsetxattr
is identical to
.Fn setxattr ,
except that it sets an extended attribute on an open file referenced by
file descriptor
.Fa fd .
.Sh NOTES
On some filesystems, such as
.Dv HFS+ ,
setting the extended attribute
.Dv com.apple.ResourceFork
will update the modification time (``mtime'') of
the file.
.Pp
Due to historical reasons, the
.Dv XATTR_FINDERINFO_NAME
(defined to be 
.Dq com.apple.FinderInfo )
extended attribute must be 32 bytes; see the
.Dv ATTR_CMN_FNDRINFO
section in
.Xr getattrlist 2 .
.Pp
The maximum supported size of extended attribute can be found out using 
.Xr pathconf 2 
with _PC_XATTR_SIZE_BITS option.  
.Sh RETURN VALUES
On success, 0 is returned.  On failure, -1 is returned and the global
variable
.Va errno
is set as follows.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EEXIST
.Fa options
contains
.Em XATTR_CREATE
and the named attribute already exists.
.It Bq Er ENOATTR
.Fa options
is set to
.Em XATTR_REPLACE
and the named attribute does not exist.
.It Bq Er ENOTSUP
The file system does not support extended attributes or has them disabled.
.It Bq Er EROFS
The file system is mounted read-only.
.It Bq Er ERANGE
The data size of the attribute is out of range (some attributes have size
restrictions).
.It Bq Er EPERM
.\" EFTYPE could be more specific but isn't POSIX
Attributes cannot be associated with this type of object.  For example,
attributes are not allowed for resource forks.
.It Bq Er EINVAL
.Fa name
or
.Fa options
is invalid.
.Fa name
must be valid UTF-8 and
.Fa options
must make sense.
.It Bq Er ENOTDIR
A component of
.Fa path
is not a directory.
.It Bq Er ENAMETOOLONG
.Fa name
exceeded
.Dv XATTR_MAXNAMELEN
UTF-8 bytes, or a component of
.Fa path
exceeded
.Dv NAME_MAX
characters, or the entire
.Fa path
exceeded
.Dv PATH_MAX
characters.
.It Bq Er EACCES
Search permission is denied for a component of
.Fa path
or permission to set the attribute is denied.
.It Bq Er ELOOP
Too many symbolic links were encountered resolving
.Fa path .
.It Bq Er EFAULT
.Fa path
or
.Fa name
points to an invalid address.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er E2BIG
The data size of the extended attribute is too large.
.It Bq Er ENOSPC
Not enough space left on the file system.
.El
.Sh SEE ALSO
.Xr getxattr 2 ,
.Xr listxattr 2 ,
.Xr removexattr 2 ,
.Xr pathconf 2
.Sh HISTORY
.Fn setxattr
and
.Fn fsetxattr
first appeared in Mac OS X 10.4.
